clk: renesas: cpg-mssr: Add support for R-Car M3-W

Initial support for R-Car M3-W (r8a7796), including basic core clocks,
and SCIF2 (console) and INTC-AP (GIC) module clocks.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Simon Horman <horms+renesas@verge.net.au>